Abstract:We have investigated the transport of light through slabs that both scatter and strongly absorb, a situation that occurs in diverse application fields ranging from biomedical optics, powder technology, to solid-state lighting. In particular, we study the transport of light in the visible wavelength range between 420 and 700 nm through silicone plates filled with YAG:Ce 3+ phosphor particles, that even re-emit absorbed light at different wavelengths. We measure the total transmission, the total reflection, and the ballistic transmission of light through these plates. We obtain average single particle properties namely the scattering cross-section σ s , the absorption cross-section σ a , and the anisotropy factor µ using an analytical approach, namely the P3 approximation to the radiative transfer equation. We verify the extracted transport parameters using Monte-Carlo simulations of the light transport. Our approach fully describes the light propagation in phosphor diffuser plates that are used in white LEDs and that reveal a strong absorption (L/l a > 1) up to L/l a = 4, where L is the slab thickness, l a is the absorption mean free path. In contrast, the widely used diffusion theory fails to describe this parameter range. Our approach is a suitable analytical tool for industry, since it provides a fast yet accurate determination of key transport parameters, and since it introduces predictive power into the design process of white light emitting diodes. 8190-8204 (2014). 30. To be sure, in a scattering system the degree of scattering is given by L/ s rather than L/ t r . Since in the vast majority of scattering systems the transport mean free paths exceeds the scattering mean free path ( t r ≥ s ) due to predominantly forward scattering [34], we consider our characterization to be on the safe side. 31. S. Chandrasekhar, Radiative transfer (Dover, New York NY, 1960). 32. M. Kaveh, Analogies in optics and micro electronics (Springer, Netherlands, 1991) 33.

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Lighting is a crucial technology that is used every day. The introduction of the white light emitting diode (LED) that consists of a blue LED combined with a phosphor layer, greatly reduces the energy consumption for lighting. Despite the fast-growing market white LED's are still designed using slow, numerical, trial-and-error algorithms. Here we introduce a radically new design principle that is based on an analytical model instead of a numerical approach. Our design model predicts the color point for any combination of design parameters. In addition the model provides the reflection and transmission coefficients -as well as the energy density distribution inside the LEDof the scattered and re-emitted light intensities. To validate our model we performed extensive experiments on an emblematic white LED and found excellent agreement.Our model provides for a fast and efficient design, resulting in reduction of both design and production costs.

An experiment is reported showing the dependency of sparkle and glare perception on luminance and area of a light source. The experimental conditions are chosen such that the results can be applied to design aesthetically pleasant LED sources. Similar to results of previous studies, probabilities of sparkle and glare perception are conveniently expressed in the luminance-area parameter space.